This Program Project's objective is to study the gastrointestinal mucosa collaboratively using both structural and functional disciplines. First we wish to document the precancerous mucosal and physiological changes after both partial gastrectomy and Barrett's esophageal columnar metaplasia. Physiological abnormalities such as regurgitation of nitrosamines, bile, pancreatic and gastric juice will be correlated with histological predictors of malignancy. Secondly we wish to study the physiological and morphological adaptive responses in the remaining small bowel mucosa after massive ileal resection and to determine the optimal oral CHO, H2O, and electrolyte mixture which will be best absorbed during the adaptive response. Thirdly we wish to compare the structure and function of the jejunal and ileal mucosa during fat absorption in order to better understand how the ileum absorbs fat when jejunal absorption fails. Fourthly we plan to gain better insight into the homeostatic role of the human intestine in iron absorption by gathering morphological and biochemial data concerning iron transport proteins and iron storage proteins within the human duodenal absorptive cells during normal, increased, and decreased iron absorptive states. Fifthly we plan studies of the effects of two commonly used laxatives on intestinal structue, function, and lipid metabolism.